>3600rpm+Clutch Engaged=Terribly Loud Noise From...?

After failing to find anybody else asking about my particular issue, I’ve decided to ask myself. I am the third owner of a 1985 Toyota Celica Supra. Nothing has been done under the hood, but last owner did make the exhaust a straight pipe (no cat, but I added a muffler) and replaced the wheels so that it requires spacers.

Ever since I bought the car in November of 2017, it has been quite loud in the cabin especially on the highway. But now it seems to be even louder than ever. Whenever I’m around 3600 rpm and accelerating it honestly sounds like a jet fighter. But as soon as i let off the gas or pop it into neutral it becomes amazingly quiet. Rev up the engine neutral as i’m coasting down the highway or at a stand still, it’s still amazing quiet. But as soon as you put it back in 5th (or 4th or even 3rd) and try to maintain your speed or accelerate, it screams. I have no idea on the decibels but it’s enough to make me wear ear plugs.

So I figure it’s not anything with the engine (since i can rev it and it doesn’t scream), nor is it wheels/bearings (because it’s dependent on the rpm’s. Even increasing speed downhill in neutral doesn’t make a difference). I’m thinking it has something to do with the driveshaft, but i can’t seem to find anything online that would support my theory: >3600rpm+clutch engaged=terribly loud noise from driveshaft(?)

Is there something else it could be that i’m not thinking about?

It could be a lot of things but a jet sound makes me think the input bearing to the transmission. Does the sound decrease a little of you go full throttle? Sometimes that bearing is loudest under s slight load and decreases with greater load and when under no-load.

i’d say the pitch of the noise decreases when i go full throttle, but the actual volume of it stays about the same

Yup, differential gears. A failing rear diff can make quite a whine (under load) followed but far worse crunchy metallic noises if you don’t fix it. have you checked the differential fluid level? Smelled the fluid? Ever changed the fluid??

Get under the car and start checking for loose driveshaft, driveshaft support bearing noises (if it has one, I don’t know) and check the diff fluid level and the pinion shaft for looseness. Pull the diff cover if the fluid is very low or smells burnt. Heck, pull it anyway if the fluid has never been changed.

Thank you guys for your input! I changed the oil in the differential but it was still just as bad. After taking it to my mechanic, he told me the ring and pinion gears were worn down. It had a bad seal and leaked oil. New differential is on the way. Again, thanks!

are you replacing the ring/pinion alone or swapping out a used carrier assy?
i see used rear ends are in the 350-550 range on ebay