I just installed a flowmaster true dual delta flow 40 series exhaust and had someone rebuild my posi unit. ocassionaly the rear diff will smack the exhaust on full compression, but I think i can solve that with new springs. My problem is I hear a relatively high pitch ringing type of sound at higher rpms and high way speeds typically in 25-35oo rpm range after this its too laoud to tell. If I stand by the exhaust at idle I can hear something similar is this the flowmaster resonance everyone talks about or did the gear guy screw up? Oh yeah this is on a 69z28 with a 12 bolt 4.10, a new m-21 4 speed. Thanks.

Exhaust can make some strange noises at times - but I would imagine it's rear gear, and look there first.

Read through this - http://www.camaros.net/cgi-bin/forum/ultimatebb.cgi?ubb=get_topic;f=18;t=000338 - and maybe do an additional search for "Rear or Gear Noise" in the Performance or Suspension areas and see what comes up.

Hope this helps.

I read that thankyou. Does anyone know how I can tell if its rearend whine or exhaust ringing? They rebuilt my original posi unit, and installed mobil 80/90 gear oil with gm additive. It only appears to be in 2500-3500 range and doesn't happen on deceleration.

dave put it up on jake stands get a buddy to run the car at where you hear the noise and get under with a hose pipe and listen all around the rear end ,axle bearings and rear cover if its in the rear end you should be able to find it.i have found a lot of different noises that way, coverter rattle to exuast leaks .hope your rear end is okay also my truck has a flowmaster on it and at 40 to 50 mph it sounds like the pipes is rattling on the fram .i looked all over the truck and found nothing wrong so its got to be flowmasters muffler