Diagnosis help - my e30 makes funny noises

Y'all met Heidi before. Well, I'm new to the e30 fanclub and my 1991 318is, 300000km makes the following noises that I am unable to google:

On the highway, tipping in the throttle causes a loud, high pitched whine up front, which I can modulate with the throttle. It loses about 3/4 of it's volume if I'm completely off the throttle, and it's not even noticeable at city speeds. Is it a driveshaft of transmission bearing? Fifth gear just ready to pack it in?

Hard acceleration produces what can only be described as fffffFFFFFFFFFPP noises from the passenger side engine compartment. It's not knock or ping. Could it be an exhaust leak?

Thanks for your help.

BTW, for anybody contemplating buying an e30, take all the recommendations on this site and multiply it by 100. I am loving this car and can't wait to carve some cones. Thanks GRM for rescuing me from my family!

Sounds like the pinion bearings in the rear differential (despite your mentioning the noise coming from the front). These are tapered bearings and get pushed forward & back when the pinion is being loaded and unloaded. This is why the noise changes with throttle application.

If you pull the speedometer sensor on the diff's cover, you will see small metal shavings collecting on the sensor.

Happened to me once and the diff is easy to change. Just find a used diff and put it in there (be sure to get a limited slip model).

Jeremy

It is not uncommon for the Getrags to lose the front transmission bearing if run low... the rear seals of the trans leak and spill the fluid, the front bearing runs dry and ... screams bloody murder. I drove one over 50k miles like that. Keep it topped it up and drive it until parts fly - a junkyard replacement is less than $250 for the whole gearbox.

The fffffFFFFFFffffpppp noise could be an exhaust leak - the union between the down pipe and converter pipe is right there under the pass side and has a pair of metal donuts that make the fitting tight... look there first for a poor fit.

As Jeremy said - could also be the rear end but... when that happens it is usually combined with a clunk on transition between accel/decel and the whine will continue if you coast down a big hill with the clutch in.