Rockford Fosgate Punch 40I Owner's Manual page 20

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. 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 equaliz-
ers) and connect the head unit directly to the amp. If the noise
disappears, reconnect the equipment one piece at a time,
making 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. Connect a new RCA line from the head unit to the amplifier. If
there is no noise, replace the RCA cable.
c. Run the RCA cable on a different route.
d. Run a new RCA line from 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 persists, see your Authorized Rockford Fosgate Dealer.
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