Engine Virbrations @ 3,100 RPM in 4th & 5th

[Highrise]

I have noticed an engine vibration in my 2002 986 (2.7L) when the RPM's are dropping and hit around 3,100. The vibration occurs in both 4th and 5th gears. There are no noticeable vibrations when accelerating, just when I let off the gas pedal and the RPM's drop. The vibrations begin almost exactly between 3,150 and 3,050.

I plan on replacing the Air/Oil separator in the next few weeks but I wasn't sure if a bad AOS could be causing the engine vibrations or not.

This 986 is mechanically stock and has never been tracked.......yet.

Thanks in advance
-Michael