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I've been trying to track down this problem. On moderate acceleration such as an "on ramp", the engine has a low pitch sound then when hitting about 3,000 RPM the engine pitch changes to a more normal sound and it feels like a gain in HP kicks in. The low pitch sound feels like a dirty filter but I have a K&N that is fine.
I've tried the following over the last few months that I would think may affect the problem:
I have a bad air filer box so I suspected air leaking, so I taped around the split
About a two weeks ago the knock sensors were changed due to random P0330 codes
Spark plugs were changed back to OEM Denso IR
IACV has been cleaned
I kinda liked my K&N drop in filter,but it was always infecting my m.a.s sensor. Plus I lost a tadd of off the line performance. So I put a purelator (factory style) filter back in and never looked back. Reset the ecm of course too.