Noise under dash after tune-up on Lexus RX300

After tune-up to my 2000 RX300 (105k miles), car came back with clicking noise under dash… took back to repair shop they agreed sounds like morse code, or like rain falling. They examined under hood and said they don’t know source, but that the work they did couldn’t be causing it. They said could be drive belt and/or pulleys, or clutch on AC, or alternator bearings… that it doesn’t look like any major issue. I brought the car in for a tune up and it came out with this annoying noise. Do I keep pushing them to figure it out what the did and correct it? Or do I trust them that additional work/expense needs to be made? What could the noise it be? It appears spread across the whole dash, but under the hood just sounds like a consistent clicking noise near the belts.

Exactly what did the “tune up” consist of?
Details should be on your copy of the shop order. If you threw yours away (you not throw them away), the shop should be able to provide you with a new copy.

Any chance this clicking could be a spark jumping from a plug boot to ground? Just wondering (and assuming as much) that the spark plugs were removed. If there’s a problem with a new plug, plug damaged during installation, or the coil boot terminal damaged maybe the spark is finding another path to ground rather outside rather than inside the engine.

It would be easy to damage a plug boot considering the age of the vehicle and the noise could appear to be coming from under the dash. Just something for consideration anyway.

The mode door servo motor is a common failure but if you show someone a noise inside the vehicle why would they open the hood and look for a belt noise? Do you hear the noise better from inside the vehicle or from in front of the vehicle?

In some position settings there may be no noise leading some to search for noises that aren’t there. Were you able to demonstrate the noise to the tech?

@‌mountainbike - The “tune-up” consisted of new spar plugs, air filter, “44k Power Enhancer safely, rapidly and thoroughly removes engine deposits”(??), oil change, and replaced 2 headlights. I have to think it has something to do with the spark plugs changed. I did notice once when fiddling with the air conditioner I turned all the air on high, then turned off - the noise went away for my drive home, but then was back. Same thing happened when tech looked at the belts (which look fine) - he sprayed some sort of lubricant on and noise stopped briefly, but then back again.

@ok4450 - I’ll have to ask them about whether could be spark jumping from plug boot to ground and whether plug boot, or coil boot terminal was damaged… interesting. Would they be responsible for that? Or would it be my additional expense to correct if that’s the problem?

@Nevada_545 - I’ll have to have them check about the mode door servo motor - not sure what or where that is :). I hear the noise inside better… not at all in front of the vehicle. We looked under the hood to figure out where it might be coming from… to me just sounded like normal engine noise, but there was a steady click, click, click near the belts… technician said sounded pretty normal. Yes, demonstrated the noise to the tech, who agreed it was strange (he said morse-code-like sounding from listening inside above the dash and in glove box - noise sounds spread across the dash to me). Tech took stethoscope to listen more closely inside the engine, but said all sounds normal.

Thanks all for your input - let me know if you think of anything else! I’ll take it in next week and let you know what they say.

"44k Power Enhancer safely, rapidly and thoroughly removes engine deposits"
they saw you coming.

Spark, you could see it clearly with the engine running at night.

Spraying lubricant on the belts is a temporary fix and should be used as a diagnostic tool only. If the noise went away when he did this, however briefly, then the problem is in that belt.


The heater/air conditioner mode door actuator/servo motor. This will be obvious it is inside the car and sound like a malfunctioning cassette tape player. While listening to the noise adjust from panel to floor and to defrost. If the noise stops for a moment this may be where it is coming from. Also try adjusting the temperature from cold to hot and fresh air to recirculate.

If your not sure it is inside the car or under the hood it may be belt noise, as this seems to be where the technician is looking. Check if it makes the noise with the ignition switch on but engine not running.

The blend or mix door motor would give you the clicking noise under the dash. Had this happen to me one time . When I selected anything but defrost it would click.

A damaged plug boot on a coil may not necessarily be the fault of the shop. Aged sticking rubber causes problems sometimes when they’re being removed for spark plug servicing. However, use of the climate control should not affect any noise caused by that.

There’s also the possibility of excessive valve lash on one or more valves causing a rhythmic ticking sound but this also would not be affected by climate control use.
It can be affected by the type of oil and engine temperatures which can make the noise rise or subside; all depending.

Valve lash should be inspected about every 30k miles but is seldom ever done.

If it is related to the climate control then I agree that a door motor could be acting up. Plastic works well up to a point… :frowning:

With moving the a/c knobs fixing it I am thinking along the lines of a door motor. Do you have a cabin air filter, if so they may have bumped something when it was replaced. Another possibilty is the brackets that go from the cylinder head to the ittake being loose the bolts for these are a bit of a pain.