2340D faint output

[Gary MN]

Output is noticeably less dark and crisp. Nothing like unreadable.
Was sharp and clear before. Am using a cheap aftermarket toner cartridge.
Wondering if this could be just a cheap toner problem or could be something else?
I don't recall this being an issue when the toner was first replaced.
I have not opened it up and cleaned the optics.

Thanks