I have purchased a EZCAP USB Cassette Capture device. My recordings have a rumble/flutter background noise. Is there a way to reduce/eliminate the noise?
Old cassette tapes can become a bit sticky inside. Try winding the tape through all the way from start to end and back again before recording it. If you have a good cassette player that works well you could try playing the tape all the way through on the good player before putting it into the EZCAP, otherwise you could wind it through by hand (find a pencil that fits into the reel hole of the cassette and start winding. Be careful with “fast forward/rewind” as old tapes can become quite fragile and you don’t want to snap the tape - also fast forward/rewind often do not wind the tape very evenly and may be wound too tight. Ensure that the play head and pinch rollers are kept clean in the EZCAP (kits for cleaning cassette players are available from many hi-fi stores).
You are never going to get Hi-Fi or even Reasonable-Fi from a device that cheap (they wholesale out of China for US$2 for high-volume order numbers).
Since you have cassettes, do you still have a proper cassette player that works properly?
If so we can advise you how to get that connected up to make Audacity recordings.