Well, there is simply something about the Audio-Technica ATR-3550 Lavalier mic that my car does not like. After trying several different mic locations, the whine/squeal would not go away; at best, it became sporadic—mysteriously disappearing and then suddenly reappearing. I finally reverted back to using the Replay-supplied external lavalier mic, and presto, my whine/squeal problem vanished.
The following video clip was shot using the Replay camera with the Replay Hard Wire Car Adaptor (external power supply) and the Replay external mic (covered with an aftermarket foam windbreaker). The mic dB on the editable text was set to factory settings—33 dB (I’ve since edited the camera dB to 59—max setting—but have not had a chance to try it out). In the video, the mic is positioned underneath the rear cover, between the fuel tank and the bulkhead. Since I have a diffuser on the car, this area is fairly well isolated from wind.
The best sound spots in the video are at 2:10, 2:50, 3:30 and 4:36. At 3:30, I do a series of quick shifts in the 5-to-6k rpm range.