The sound is a zipping or like a low pitched prolonged honk. It sounds like rubber pressing against something that is rotating fast. No screech at all.
It only happens under hard acceleration, generally going uphill. It happens when accelerating from a stop or when accelerating while already going 20 or 30 mph or at highway speeds.
It does not happen every time I accelerate hard. I'd say maybe 10-20% of the time. I can't figure out a way to reliably reproduce it and I've tried pretty hard.
Once the sound starts, it lasts while I keep my on the gas. The sound persists if I accelerate. If I let my foot of the gas, even if it's just for a second and then I immediately reapply, the sound goes away. It's almost like two parts are slipping and if I give them time to catch up the slipping goes away. That makes me think it's something in the transmission, but I don't notice any power loss while it's happening. The transmission fluid looks fine but I haven't replaced it. I tested the viscous coupler and it also seems fine.
I thought I had it nailed when I noticed the muffler was rubbing on the driveshaft due to broken exhaust mounts. I replaced the mounts, but the problem is still there. It might be slightly better but it's hard to tell with how random it is. It was extremely difficult to rotate the exhaust back to where it should be to get the mounts on. Also the rubber mounts look like they're straining to hold the muffler off the driveshaft, so maybe that's still the issue? I don't have an OEM mount at the tailpipe since the PO cut off the resonator, so maybe it's not held in place properly. I definitely have a mean whistle at high RPM due to the lack of resonator, but this is a different sound than that.
I've had the sound since I bought the truck. Since then I've done a front and rear axle service including brakes. I've replaced the u-joints and had the driveshafts balanced. None of those things made any difference.
So there's my long winded explanation. Anyone else have symptoms like this or have ideas what it might be?
It only happens under hard acceleration, generally going uphill. It happens when accelerating from a stop or when accelerating while already going 20 or 30 mph or at highway speeds.
It does not happen every time I accelerate hard. I'd say maybe 10-20% of the time. I can't figure out a way to reliably reproduce it and I've tried pretty hard.
Once the sound starts, it lasts while I keep my on the gas. The sound persists if I accelerate. If I let my foot of the gas, even if it's just for a second and then I immediately reapply, the sound goes away. It's almost like two parts are slipping and if I give them time to catch up the slipping goes away. That makes me think it's something in the transmission, but I don't notice any power loss while it's happening. The transmission fluid looks fine but I haven't replaced it. I tested the viscous coupler and it also seems fine.
I thought I had it nailed when I noticed the muffler was rubbing on the driveshaft due to broken exhaust mounts. I replaced the mounts, but the problem is still there. It might be slightly better but it's hard to tell with how random it is. It was extremely difficult to rotate the exhaust back to where it should be to get the mounts on. Also the rubber mounts look like they're straining to hold the muffler off the driveshaft, so maybe that's still the issue? I don't have an OEM mount at the tailpipe since the PO cut off the resonator, so maybe it's not held in place properly. I definitely have a mean whistle at high RPM due to the lack of resonator, but this is a different sound than that.
I've had the sound since I bought the truck. Since then I've done a front and rear axle service including brakes. I've replaced the u-joints and had the driveshafts balanced. None of those things made any difference.
So there's my long winded explanation. Anyone else have symptoms like this or have ideas what it might be?
