You are still making assumptions without facts. For
example, if the key is on but engine not running, then
regulator electronics inside the alternator can still be
radiating RFI. Obviously. Engine need not be turning for
those electronics to be functioning.

Furthermore, its not about something "not grounded and
giving off static". It can also be "something grounded
differently and therefore radiating noise". Noted earlier -
every ground wire is also an antenna. Vehicle electronics
must be grounded to work. Therefore even working electronic
device that radiates noise is also grounded.

There is no way to visually confirm a connection - "the
connection to the radio appears good" and yet that antenna
connection is not between two connectors of the same size. A
failed antenna wire connection will always 'appear good'.

Welcome to an art where you cannot make blanket
assumptions. Your first efforts should only be on confirming
antenna integrity as I and Jim Adney have noted. This, of
course, assumes everything is original Jeep equipment - a
necessary fact which has not been stated. For example, if
that amp is after market, then there is a grounding change -
or other problem.

Again, welcome to an art where everything you do must be
understood experimentally AND must also be in total agreement
with theoretical concepts. Your assumptions such as the
connector 'looks' good is begging to not have a solution.
Good reason why EMI/RFI experts have decades of experience.

wrote:
Thanks for all the advice. Let me fill in some more details. The radio
is OEM in a 95 Jeep Grand Cherokee Limited. It has some sort of
amplified output and an electric antenna. The problem has been more
progressive than sudden. Only affects reception when the car is 'on'
(running or key in the on position). The antenna is original, and the
connection to the radio appears good. Something else not grounded and
giving off static is a possibility...would have to be something that
powers up just with the 'on' switch, not just when running (may
eliminate alternator). If it is a 'ground leak,' might that explain how
sometimes fiddling with an electric switch seems to reduce the static?
Maybe the other switch grounds some of the static causing emission? Not
really knowledgeable about electronics.