Ohhhh.
Radio Shack and Olsen used to sell these things cheap before the improvements in
vehicle electronics. All I remember about them was they were tuned to the basic
frequency of the vehicle's electrical system. I don't know if this is a home project,
or if you have a commercially built system. If it's commercially built, the manufacturer
would know what to recommend to overcome this problem.
It's been twenty years since I worked on this type of a problem, and can't think of a
recommendation off the top of my head.
I'll give it some thought, and repost if I remember what I did in the past.
What you might consider, is what signals the motor noise is interferring with.
Multiple pieces of equipment, or just one.
You can limit the noise from the motor. Or I think I would be more concerned with
filtering the input power to your equipment you're picking the noise up on.
(Unless this motor noise is actually so bad it's being picked-up on some type of
audio gear through it's signal input wires or antenna).
Have you isolated the antenna or input signal from the chassis the motor is connected
to?
How sensitive is the equipment? Is this a radio transmitter/receiver, or audio device
of some type?
Do you think the noise is coming-in through the actual power wiring, or is it induced
through the air from the motor due to motor proximity to your electronics?
It's easier to attack the problem, when we know the source transmission medium.