help please
With that aside, it sounds like you didn't use the correct wire for your remote lead. After the head unit is turned off, the output of the amp is not cutoff right away. What you're hearing is the amp bleeding off any stored energy.
Generally, the remote turn on input of an amp not only turns the amp & output stage(s) on, but conversely turns the output stage(s) off right away when the HU is powered down.

