Mystery 30 Minute Sound Degradation

I come to you experts with a recent mystery. For the first 30 minutes after I turn on my system, and whether I am using my tuner or Bryston BDP-1 through my W4S DAC2, the first 30 minutes or so of playing the music is thin and shrill, and I have to turn up the volume about 50% more than usual to get the same sound level as I used to get.

Possible contributing factors, though I lack the technical knowledge to know why or if:

1. Upgrade to Solen teflon cpacitors in my pre -- Wyetech Opal about 2 weeks ago;

2. Insertion of HiFi Supreme Tuning Fuse in pre a few days ago. I am virtually certain (but will check again) it is the right size and amperage and that it is inserted in the right direction.

The condition was sporadic before fuse replacement but now it consistent every day.

After about 30 minutes, the sound quality and volume returns to what was its normal wondefrul state.

Any thoughts? Thank you.

Neal