Same thing here...don't know why it only happens when it's warm outside but every time I begin seeing it I give it a good spray with canned air and it goes away until another speck of dust works it's way in. Electronics grease would probably work well

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth