yes, but if it's turned on and you make your settings you might notice hiss in record mode. suddenly you might think your A/D converters are broken. but it's all good, you just have to turn master compression off. when i've noticed it, i've searched the web and there are forums where exactly this "problem" was described generated by turned on master compression. these users of the 500 might have sold there unit declared as faulty on ebay.
yes me too, but for me it's barely noticable and i don't find it disturbing. also check your mixer settings or whatever you have connected to your input. the hiss in record mode when master compression is turned is much more significant and disturbing. it almost sonds like feedback.
Well it does make sense that the noise would be more noticeable while the compressor is on.
If your familiar with the way compressors work, ( and I'm not an expert but I do understand the basics) then you should know that when you increase your make up Gain then your noise floor will be raised.