Here are the quotes from Todd about the "rays" that I have seen so far.

http://www.bbcboards.net/showthread.php?t=770882

He doesnt mention the PS31 specifically, but I would have assumed it would behave more like the PS30, but maybe not. I cant remember anyone saying they saw the rays on a PS31 so far. Maybe he will chime in.

Donnie, sorry it took a while to respond to this thread. I was waiting for the lead Panoptix engineer to get back in after the holidays. He indicates that the trolling motor interference you are experiencing (2 or 3 weak lines) is normal, and results from the methods used to reduce bottom clutter. I have had the exact same interference with my PS21, and as you indicate, this minor interference does not affect how I use it at all (doesn't mask any fish or structure).
Relative to PS30, it also has the same type of trolling motor interference, but it presents itself in just a single line, mostly off the edge of the view.

Also note that when you run a PS21 and 30 at the same time, this can also cause sonar interference (in addition to potential interference from trolling motor) that behaves as I stated earlier where the 21 shows it as potentially 3 lines and the PS30 shows it as one line to the side. This isn’t a defective situation or anything, just acoustic interference.
In JordanC's case, I wouldnt call those "weak lines", but that could be due to his settings - Trials on, Hi Gain, low noise reduction - and/or possibly an especially bad trolling motor that puts out more interference.

This is a case where it varies a lot from one setup to another, which makes it difficult to pin down.