Loud noise when driving over 30mph
 

Hey guys, I'm stumped. I drive a 1991 convertible with about 110k miles. At around 30 mph there is a reasonably loud hum that even overpowers the engine's noise. It gets louder and more pronounced as the car gains speed. I've noticed that letting up on the accelerator will slightly decreases the noise. Also, and this is what's really stumped me, is that when I'm turning left, the noise completely disappears. But as soon I let go of the wheel, the noise returns. I've checked the muffler and there were no holes or leaks. And I've been driving likes this for a month. I have not noticed any discernible difference in performance, handling or gas mileage. Any insight you guys could provide would be greatly appreciated. Happy holidays!

have you changed your tranny fluid? it may be the tranny, not likely but couldn't hurt to check.

Check the wheel bearings... normally that would sound like a bad front wheel bearing.. or a possible noisy rear diff..

The turning makes me think Wheel bearing though...

if you turn left it is possiby the right wheel bearing.. because when u turn left the force is applied to the right side of the car... this would load the pressure on the right wheel bearing cause this hum/growl

if theres a vibration with the hum, check rear diff... do rx7s use U-Joints?

all good tips, also look into our suspension components to make sure everything is tight. Check your wheel balance too.

im gonna go with bad wheel bearings

I had the same problem with my '89 vert. I slid into a curb and bent the front subframe. Passenger side front wheel is out at the top and in at the bottom-looking from the front. Is that negative caster?
I replaced the front subframe and it quit making the noise-almost like a roar.
When I turned to the right the noise would go away until the wheel straightened out.

Wheel bearing would be my guess.

+1 on wheel bearing, makes me think that cause it makes more noise at higher speeds.correct me if im wrong but, suspention i would think would be all the time.
drive beside a fence and the noise will be easier to locate. works for me

Ima guess wheel bearings. I had similar problem, though not as loud. Disappeared when i turned right and it was the right wheel bearing, IIRC. Or I might have it backwards. Anyhow I replaced the front wheel bearings on both sides, since I figured the good bearing probably didn't have too much longer to live anyway. I noticed a badly kinked grease seal spring in one. I couldn't see any problems with the bearings themselves. So if I or the P.O. followed the basic scheduled maintenance - clean with a solvent, let dry, inspect bearings, repack grease and replace grease seal - then maybe that would have been enough. I'll never know.

The Mazda dealer did not have OEM replacements, btw. You need the whole expensive hub or something. So I got the bearings and grease seals at the local auto store. There's inner and outer bearings (1 of each per wheel = 4 total), plus grease seals for the inner bearings.

I had a similar noise on my 240sx once and it turned out to be the diff leaked all the fluid out and was humming really loud the faster i went, by the time I found out what it was the diff was ruined.

Yes they do.

Hey guys, thanks for all the responses, I've actually been away this pas month so I haven't been able to check up on the thread. I'll check the wheel bearings, but how do I tell if they're the real problem?

Front wheel bearings on our cars are maintenance items. They're supposed to be removed, cleaned, greased and reinstalled (and tightened with a proper pre-load). Once they're worn, this won't cure them and you'll still have play even after setting proper pre-load. The rears are not serviceable - once they're worn, you have to replace them, which involves pressing the old ones out from the hub.

Put one corner up at a time and spin the wheel. Listen for noise, check for play. Compare to the others. I left some things out since I hope you have the FSM and will read up on it (FSM in my sig.).

Could be something else but from what you said (increasing noise, while turning goes away, etc.) I'd first check the wheel bearings. After that, I'd check tires, steering linkages, balljoints, etc. This is a dangerous area to screw around with or let things wear out, so if you're not confident at any time, take it to a good pro, IMHO. GL.