Camry :: Grinding Sound At Around 1400 - 1600 RPM / When Starting From A Dead Stop

I have a 2001 Camry LE, 4 cyl, 2.2 liter, automatic transmission, 163Kmiles on it.

I'm hearing what sounds to me rather like a grindy sound at around 1400-1600 RPM. Initially the Camry seemed to do it only after getting into 2nd gear at about 10MPH, but now i see that it is associated with RPM and not the gear so much (the noise is less frequent and less loud in 2nd and 3rd gear- not noticing it ever at above that). I should say that the Camry has been making lots of noises since a new exhaust was put in by a cheap Bosnian shop.

It seems to only make that particular grindy noise when starting from a dead stop, but not if i was already coasting at all. So far as i can tell it seems to only happen about half the time- if I'm accelerating very slowly it doesn't seem to happen much. If i start climbing a hill after a dead stop it seems to come on fairly reliably.

It does not seem to make the noise when passing down through 1600 RPM while slowing down or revving down.

When i started the Camry up today, the noise cropped up well before i got to 8MPH (where it typically shifts into 2nd gear). Which is to say the noise appeared before it even started to shift out of 1st gear.

If i stay in Drive or Reverse and apply the brake so as to not go anywhere, the noise generally starts around 1600RPM. Since the car isn't moving, i think this might rule out the transmission. I hope.

However when in Neutral or Park and i bring the engine up to 1600RPM and beyond, the noise does not appear. So that's perhaps not so good. Of course my car idles a lot better/smoother in N and P than it does in D or R. It's rather rough idling in D and R.

I'm hoping maybe it's a vibration issue- something like harmonic amplification- where something only rattles in a certain frequency range. I pulled up next to a brick wall, kept on the brake, went into D and got up near 1600RPM and the reflected noise does strike me more now as maybe being less a grindy noise and more of a rattly vibration.

The Bosnian shop who fixed up my exhaust were too quick to dismiss the noises i heard after they worked on it. I think maybe something is loose. I hope. (I could feel air leaving the flexpipe's woven area itself but don't know if this is normal.)

Going up hills increases the likelihood of the noise appearing (so i take this to be suggestive that it IS the transmission).

However on a flat road if i hit the gas to quickly get up to 1600RPM before I'm any where near auto shifting out of 1st gear, the noise also usually appears (so i take this to be suggestive that this is not the transmission). I've also gotten the noise to not appear until well into 2nd gear.

The fairly-repeatable noise appearing in the 1600RPM zone regardless of my gear position gives me some hope that the xmission is not the source of the noise. So on balance, i think there's some indication it's the transmission, but there's also evidence that the source is other than the transmission.

The noise does not occur in Neutral or Park while revving up to 1600RPM. But then too, the engine, exhaust and vibrations always seem considerably less in N or P, as opposed to being in Drive (or Reverse). Why my Camry is quieter and more smooth in N and P as opposed to D or R? In the latter two modes, i imagine the transmission is engaged? And that the transmission is unengaged in P and N? And would that make the car louder or vibrate more, at least under certain conditions? Is the engine under less load in P and N?

And are noises at certain RPMs in D or R, but not in P or N indicative of Transmission problems? I notice the shop overfilled the transmission fluid every time i've had it changed.