Warm Audio WA-8000 Large-diaphragm Tube Condenser Microphone

I bought this tube microphone because I was impressed with the way it sounded in demos and I always wanted a tube microphone from the WARM company. On the first day I noticed a static/hum like sound coming from the microphone. It wasn't my interface and there were no nearby electronics or cables that could cause interference. I was finally able to place the microphone at such an angle where the noise was minimized or gone. Still wanting to give the microphone the benefit of the doubt I proceeded to use the it at the proper settings and recorded some beautiful top end voice overs..and it was gorgeous sound. The second problem developed when I noticed that the longer I used the microphone the less dynamic it sounded. It started to sound harsher and had lost some clarity. Was the tube heating too much or was there a defect in the production of my particular microphone? So, between the tube noise issue and the unreliability of the sonic consistency I had to return my microphone. P.S. I also own a Mojave brand tube microphone that has never had such problems, and delivers great sound consistently during my longest recording sessions.