Anyone else experienced this Knocking sound under right foot?

[Donnieshacks]

So... I have a 2019 RTL, second owner, 2400 miles or so. I did a bunch of upgrades and also just had 2 front tires done. Alignment, and oil change. One tire had a screw in it, and I decided to put on car tires. Huge difference and I love it. 1st owner changed the oil at 1800 miles or so. I knew it didn't need to be done but did it anyway. I used Rotella T6, which is what the previous owner changed it to at 1800 miles. He also installed a BajaRon sway bar. The issue I'm having is there's a sort of knocking sound when I coast to a stop, foot on the brake, in 1st gear. It comes and goes, but I notice it when the engine is hot, and I've been riding a bit. As soon as I lift my foot off the brake to take off, it's gone. It sounds like the engine, but I can't tell. It runs and shifts great otherwise.

I've done a search and saw 2 things - one guy said same thing happened to him and it was after changing to oil and to a full synthetic non-BRP oil. He thought it was the clutch, but he never continued the thread, so I didn't find out what it was.

A second thread was people talking about sway bar nuts being loose - especially the upper right. I haven't looked into that yet, but I just wanted to put this out there to see if anyone has experienced the same thing.

Oddly enough, I had a 2018 RTL with 7000k roughly that did the same thing just before I sold it. It only had BRP oil, so I really don't think it's that. It also had the upgraded sway bar. Any info would be great. Thanks!

[BajaRon]

Sway Bar issues are easy to determine. Simply stand on the foot pegs/floorboards and rock the Spyder back and forth vigorously. If anything in the sway bar system is loose, you'll get a clunk (loose bushing bolts) or clink/clank (loose end link bolts). If you get none of these sounds. Then you can move on to another possibility.

[Donnieshacks]

Thanks! Good place to start. On my 2018 when this happened, my radiator overflow sprung a leak shortly after. Not sure if that was connected at all. I sold the bike shortly after that.