I recently bought a digital piano. The grand piano sounds awesome. But after playing for like about 10 minutes, it started to sound funny like its coming from a tin can, I cannot describe it. It's not severe but noticable. I use Yamaha EMX5000 powered mixer and JBL 115 15" speakers. The piano sounds from my other synthesizers all seem to have this problem so it's not partaining to this digital piano alone. Does anyone know what I'm talking about? Thanks in advance. Willie.