Check for crankwalk. That sounds exactly like what mine just did a couple months ago. The noise quieter until after 2500 rpms, then it would get louder or until the car warmed up, Also the car ran fine except the knock sensor was pulling timing after 3000 rpms due to the noise so it was losing some power. I tried everything to get rid of the noise and it ended up being the main bearings and rod bearings.
None of the usual signs of crankwalk were there, such as the clutch pedal dropping to the floor or anything along those lines.
I was having a hard time pinpointing the noise, at one point it sounded like it was coming from the transmission area, so i changed the clutch and checked everything. Still the noise was there.
Changed out the lifters to the no tick ones and bled them, noise still was there.
Retorqued the head, and cams. Still there
checked the CAS.
Then finally pulled the oil pan and found the rod bearings were completly fucked, and the main bearings were pretty much out of spec. I ordered rod bearings from MAP but it was too late. I drove it to a meet and on the way there complete crankwalk, Then i parted out the car.
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