"Problem develops over time" was exactly what I was having too with the 3 APP1 pairs I ended up using over time. A gentle blu-tack treatment got rid of it every time though on my last pair. The side mesh against the ear needed a regular maintenance routine. Now rocking APP2 with no such mesh and no issues whatsoever. I'm sure a lot of people would find the problem gone with APP2s. FWIF.
You say blu-tack treatment got rid of the noise every time. So what do you think is causing the problem? Earwax that is stuck on the mesh? Is this the mesh that is on the plastic hardbody of the earphones, or the removable mesh that is part of the ear tip?