Are you observing what you mention on the tach? If the tach does not indicate the engine is revving, then suspect that the fan clutch is engaging. The added engine compartment noise can fool you to thinking the engine speed has increased. If this is the case, suspect a cooling problem.
Steve
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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7
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