The uncommanded HVAC blower speed change is back... in automatic or manual mode the blower will suddenly, and briefly, increase speed (to max?), although the blower speed indicator on the push button control unit remains unchanged. Along with the speed increase is the sound of perhaps a flap cycling, resulting in increased back pressure on the blower.

The cabin air filter and blower motor resistance unit have been renewed.

Any ideas as to what the problem might be? Push button control unit?