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?