Time to check your auxiliary radiators...

[neckarsulm]

Cleaned mine out today, vacuumed out the loose debris, then using a Wurth detailing brush, brushed the fins which released a load of dust and small bits which I vac'd out. Then I sprayed some WD40 type stuff on there to protect and bingo.

[wolfgang]

Checked mine today and they were, thankfully, clear of debris. I cleaned the grilles using Megs APC and clipped them back on. This'll become part of my washing routine from now on as it's a very easy thing to do.