I've got the same issue on my 22 90 V8. Doesn't happen all the time, but circumstances you are highlighting are similar. I have no aftermarket parts. I brought it in once and they couldn't replicate but now I am headed out of warranty (only 26k miles though) and I am going to force the issue. Will let you know what I find.

Do you have anything you've seen on the internet on any successfully seeing it fixed?