Rockford Fosgate 4-CHANNEL AMPLIFIER - Manual (Page 30)

Problem
Engine Noise (Whine)
Solution
1. Disconnect the speakers from the amplifier. Connect
a test speaker to the amplifier output terminals. If the
noise goes away, check your speaker leads, speakers
and crossovers.
2. If the noise persists, use a "shorting plug" to mute the
input signal at the amplifier. If the noise goes away:
a. Bypass all of the other equipment (i.e., crossovers
and equalizers) and connect the head unit directly
to the amp. If the noise disappears, reconnect the
equipment, being sure to test for noise after each
install. Logic indicates that the last unit installed is
the culprit. Refer to the unit's owner's manual for
more information.
b. If the noise persists, connect a new RCA line from
the head unit to the amplifier. If there is no noise,
replace the RCA cable.
c. If the noise is still present after replacing the RCA
cable, run the RCA cable on a different route.
d. Isolate the grounds in your head unit so there is
only one grounding point. If the noise disappears,
install the radio, using only one (1) grounding point.
Isolate the radio chassis from the grounding on the
dash, and use an antenna grounding loop isolator
on the antenna.
If noise still persists, see your Authorized Rockford
Fosgate Dealer.
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