High pitched humming on start up

Just picked up my car from the shop last night. Had a full tune up, air filter replaced, radiator upper hose replaced (was leaking), transmission service and an oil change . When I picked up the car at night I heard that it sounded a little off when starting but I was so excited to have it back that I drove it home. Once I was on the freeway, no weird noises and it drove perfectly fine. This morning when I started it up again the sound was there again. I can only explain it as a sort of high pitched humming. I pulled away from the curb and it made more noise - I heard that sound once when I needed power steering fluid. I put the car in park and popped the hood. Power steering fluid was full. My mom suggested I restart the car so she could hear the sound. This time when I started the car it sounded fine. Typical.

I drove it in to work and it drove fine and never made that noise again.

Any ideas?

(car is a VW Passat 01’)

Go to your owner’s manual and read the protocol for checking the tranny fluid level. Check the level.

The sound may be nothing, but since you had the car serviced it’s a good idea to check the fluid levels out. It’s actually a good idea to monitor them anyway, but after servicing I always double check them…just in case the mechanic took a coffee break in the middle of the job and lost track of where he was.

It’s also possible that when he serviced the tranny he dripped a bit of fluid on the serpentine belt. Perhaps you’ve just “burned off” some fluid residue from the belt’s surface. Take a peek at the belt and see if you can see any spotting from fluids.

Post back.

Next time it does it at start up, pop the hood and listen to all the belt driven equipment to see if its one of those. Also check the air filter lid and make sure it’s seated properly and not sucking in air via a small crack making a whistling or humming noise. Good luck!

If the noise is there when you first start it but then dies off after a minute or so, I would believe you’re hearing the air pump.

You could ask your mechanic to use a length of garden hose as a probe to narrow down where the sound is coming from.

I also have a passat 2.0t. I do have a whirring sound. Which comes from the a/c pump. Very possible when you hear this. You have your defrost on which inturn turns your a/c on automatically on some models. Other models you have to manually hit the a/c button. the a/c pumps on these are known to be a little on the noisy side. If you can turn your a/c on and off. to see if the sound goes away or comes back.
Hope this helps…

By the way im not sure whar model you have. But most of the passats had a non servicable fully sealed transmission. If your model has this go back and get your money back for that. Since there is absolutely no way to service the tranny on the sealed units. You can find out if your model has a sealed unit by just swinging by the vw dealer and asking them. Or call them with your vin# to determine.

@vwfan, not sure what you mean by a fully sealed non-serviceable transmission. Every VW I’ve ever seen has a serviceable transmission. Sure you need special parts and tools to do it, but I regularly service them.


I’m a professional mechanic

There is no such thing as a “non servicable fully sealed transmission”

Pure marketing BS

There are tools and procedures to service all automotive transmissions

The noise you hear might be coming from the secondary air pump.


The secondary air pump is just a motor with a fan. This intoduces air into the exhaust system so the catalytic converter lights off faster. One of the indications that the secondary air pump bushings are wearing out is a high pitched noise at start-up.

The transmission fluid in your sealed transmission can be serviced with a transmission fluid exchange machine.


Good grief . . .

When I was still at the Benz dealer, every once in awhile some customer would come in complaining about a whining sound every morning, and it would only last several seconds

The thing is, though, the noise was absolutely normal. It wasn’t indicative of anything

It was usually the secondary air pump. It was made by Bosch, and looked a lot like the one in that picture


Anytime a rotating component starts making noise, you know it’s not going to get any better.

Did the pump make any noise when the vehicle was new?



I have a 2005 Camry with an automatic transmission. Toyota says it doesn’t need to be serviced

It has a dip stick and a drain plug . . . but the engine bay picture in the owner’s manual doesn’t show the transmission dipstick


Read this . . . they don’t mention how to check the transmission fluid level, yet if you pop the hood, you can see the dipstick





They all did that, brand new, from the factory


Well, if they all did that brand new from the factory, why is the OP all of sudden complaining about the noise?



I was a Benz mechanic

OP has a VW, but that pump looks extremely similar to the pumps that Benz used

Bosch made the pumps for Benz . . . Pierburg made the pumps for VW

Without being able to hear it and without hearing back from the OP, I find two things to be equally plausible. One is that there is a new problem, such as a noisy secondary air pump announcing its age. The second is that VWgirl09 had just had a bunch of work done on the car and was overly vigilant / sensitive to sights/sounds/feels and suddenly noticed something she’s never noticed before.

Which it is we may never know.

Maybe you can service most of these tranny’s. But when i purchased my passat. I wanted to get the transmission serviced. I went to tge transmission shop asked for a service. They informed me it is fully sealed. Cannot be serviced. I thought they were full of it. So i went to the vw dealer. They infact told me there is absolutely no way ti service the transmission in my model. It is fully sealled non servicable. The transmission has no fill holes…drains… Ports…nothing. All it has are the output flanges for the stub axles. If there was a to service it im surprised that no one would be happy to take my money for the procedure.


The dealer is lying through their teeth

There is no such thing as a fully sealed, nonserviceable transmission

As I said before, it’s pure marketing BS

The idea is to sell cars that supposedly need less maintenance

So… my saga continues.

After I picked up the car, I drove it around for the weekend and tried to ignore the early morning high pitched sound since it seemed like most of the initial comments on here made me feel like it probably wasn’t a big deal and also the car drove fine.

Fast forward to Monday morning when on my way to work, CEL starts to flash and car says “STOP” in big red letters on my dash and the coolant light pops on. After cursing for a sec, I find the nearest Chevron and buy some coolant. Pop the hood open and the damn thing is down at the “minimum” line. I top it off and continue on my way. Call the shop and tell him what happened. He says to check and see if there’s another leak (mind you, a coolant leak is why I took the car to him in the first place and he had supposedly fixed it by replacing a hose). So I tell him that I’m not checking shit and I take him the car during my lunch break for him to look at. On my way to the shop, coolant light turns back on. I keep my eye on the gauge and drive to the shop like that (shop was only 10 mins away). When I get there they put it up and now say that my water pump is broken. WHAT THE ____! He tells me I shouldn’t drive the car like this so he’s gonna fix it and gives me another quote of $700 (I had just paid him $800 the previous week). Feeling helpless, I leave him my car. That night I talk to an old friend who knows about cars and he tells me point blank that I’m getting ripped off.

Anyway… I have my car now, it seems to be running fine and I’m never ever going back to that mechanic again. Only reason I went to him was that he is my friend’s dad.

OH! And about the high pitch sound - when I picked up the car the mechanic said he noticed it too and that it was some hose or something in the power steering (at this point I was so irritated by him that I wasn’t even listening to what he was saying). Anyway, he said he replaced it “free” and I haven’t heard the sound since.