I saw a DIY info on sliding door a while back here. See that stuff on opening while in gear and fixing loose contacts. The contacts might need cleaning or door just recalibrated. Mine also does that and I have to do this too. On bumps or sometimes just because it makes that warning noise. I will see if I can find the link (think from the official thread sticky).
Intermittent sliding door open-door alerts while driving? Happens when turning or over bumps. You checked and the door seems snugly closed? I've had this problem repeatedly and sometimes this or that seems to work and sometimes not. I've tried manual reset and reset with the door switches on the dash console. I've tried pulling the fuses. But I finally determined that, when the prob occurs, I can manually detect a slight stickiness in the contacts in the door and door jamb -- these are the contacts that signal the computer that the door is closed. There is an array of them on the door and mating ones on the jamb. These are not simply stationary contacts; they are spring loaded. If they are the least bit sticky, you can get door signal problems/alerts.
If you have the probs, check these switches to see if they move very freely. They won't be very sticky and cause the prob. If they are very sticky the problem won't be intermittent. If they are jsut a tad sticky, then then one or more of the contacts between the door and the jamb will be poor, resulting in the the flickering light that is susceptible to strong vibrations weight shifts like bumps or turns.
I recommend using a silicone spray because, unlike e.g., WD40 and other lubes made from fish oil, it won't oxidize, dry out, and lose lubricity. This has been the most consistent and long lasting fix I've tried.
On the door side the contacts are spring loaded inside a plastic sleeve and the sleeve is spring loaded too so be sure to lubricate both surfaces on each contact. On the jamb, there is only the sleeve to lubricate. Lubricate liberally with a high quality silicone spray. Use a tube on the spray can so you can avoid over-spray and wipe all the excess off of the contact mating surfaces with an absorbent paper towel -- this will also help clean off any dirt from the contacts although that was probably the first thing you tried as a fix -- but it can't hurt.
But, do you know how hard I looked and how long it took for me to find a good answer? Even the Dealer wasn't a big help and I paid that guy real money! With that in mind I posted in the several different threads on the same issue. If the matter only came up on one thread, that would be simpler for everyone, but things don't usually work that way. Admittedly I could have posted links but it was just as easy to post the text, which will also be easier for the reader. IF people search through any of the threads except the the only one with that particular solution offered, I fear some will go through as much pain as I did until I found something that actually worked reliably and consistently.