Reduce output

Question

I recently notice the the output from my receiver seems to be reduced. When playing music I would have the volume set at -.50. This was plenty of output for easy listening. Now I find that this setting appears to be putting out less sound. I've checked all connection, all channels, each individual speaker and tried different sources of input (radio, cd, dvd)but have the same results. I can turn the volume up to get the output but am concerned on the cause of the reduced output?