Lately I get a "Groan" from my engine as it passes through from 1400 RPMs to 2000 RPMs. I have ruled out axles as the problem because it occurs at a standstill or while driving. Basically, you hear normal engine sound as you accelerate and then it takes a different tone. After 2,000 RPMs the sound turns back to normal. I am at the 90,000 mile mark. I have maintained the vehicle well, but have not yet performed the BSM or TB change. I am suspecting that it is the motor mounts given that this sounds like a harmonic problem to me. I've looked at both motor mounts and I see no visible sign of wear. However, in my experience with other cars, mounts can compress or otherwise lose effectiveness. You can't notice it until you compare it to another brand new mount. Any advice?