If the noise is in both channels then you should look for something common to both channels. Capacitors are the likely cause, but some IC's might cause it. You say that the volume control doesn't effect it, if that is the pre-amp's volume control then the fault will be after that part.
Remove the power plug first, try to find the Battery inside the unit,Remove it, just for a minute, or two, and put it Back, hope it work again.if you don,t find in the users manual ,how to reset !
If your cd player gets older there can be a timing problem by several causes like a slipping belt, or a dirty mode select switch somewhere or a microswitch that is not functional by the slipping belt too long time to take the cd to inside and push up the platter and mechanic to give the focussing of the laser to read the table of contents on the cd , that the cause in 90% microswitch cleaning by contact spray under the tray and on the beginning point wheren the laser begins its start cycle to focussing and give a turning respond to the spindle motor thereis a little microswitch it pushed in or an other switchable point also under or near the cd tray another where the detection is the start that the cd tray is closed and the laser start to focussing on the cd surface and give the cd a turn for the toc and then when its timed correct it recognized and displayed the track position highest priority is that rubber belt that driven the tray and the 2 or 3 microswitches or contacts you should find what have functions in the intake traject. in a short time all together. little suggestion whats meaning Denon DCD815 CD Player disk tray wont open or copy this link https://www.youtube.com/watch?v=H9AbnvF1www
