Not sure if I noticed this before cuz sub was in the boot of my fiesta, but now when I turn off I get a Bump! noise through the sub.

My amplifier is a high quality one Pheonix Gold Tantrum series 400.4

(4channel amp running front door speakers and other 2 channels bridged running sub which sounds lovely)

Its a shame its doing it.

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hardly used but 3 years old.

Any help??