Odd noise with FT-1802

[KJ4BRI]

I have an FT-1802M installed in an 01 Isuzu Trooper. I installed it in place of a cheap Radio Shack scanner. (same antenna wire) The Radio Shack scanner never had any ignition noise. I ran the power wires directly to the battery, (and later added a 60amp alternator noise filter).

The noise is only present on frequencies in which I can transmit. For instance if I tune in the state police on 159.000mhz there isn't any noise. If I tune in 146.91mhz I get noise both when the squelch has been broken and when it hasn't been broken. In both cases the noise is a buzzing that increases with engine speed. The noise is much louder when the squelch has been broken.

Any suggestions?

Thanks,
Tad