Noise / interference disappears with sustain pedal pressed

[lukevintage]

I'm still a novice on the piano so currently rarely play using the sustain pedal. In fact, it wasn't even connected for a period as it got in the way, collected dust, and was another thing to remember to remove/insert during repair work.
Now that it's back on and my piano teacher is pushing me to use it, I noticed that the very light noise interference would disappear once the pedal was fully engaged.
The piano was super silent when I first bought it. I have since brought it back to life by cleaning out all the dust, key dip, key level, and played with the voicing / pickup position. I also bought a Speakeasy suitcase pre amp. I thought the interference was coming from the pre amp, especially since it was so intermittent. However, I now believe it is the piano itself.
There is a lot of interference when the harp is not screwed onto the supports. I assume it is grounding through the screws.
What are all the causes of interference on a rhodes (mine is 1979 MK1)?
Why does engaging the sustain pedal reduce the interference?

[spave]

Does your damper bar have a ground to the RCA jack?

I've never heard of anyone having that exact problem before but there have been similar problems over the years that seem to have been solved by the damper bar ground wire.

https://ep-forum.com/smf/index.php?topic=3480

https://ep-forum.com/smf/index.php?topic=2683

https://ep-forum.com/smf/index.php?topic=7102

https://ep-forum.com/smf/index.php?topic=6999

https://ep-forum.com/smf/index.php?topic=7095.msg35859#msg35859