1 out of 4 cassettes won't record

2.0.6 on OS X 10.11.6
Converting 4 cassettes. Marantz tape deck RCA (red-white) connected to 2009 iMac line-in with 1/8 inch jack. All cassettes sound good when played on the Marantz. First 3 cassettes sound good when converted using Audacity. When I tried to convert the last cassette I just get white noise with a VERY faint recording, like it’s far, far away. This 4th cassette is TDK from the UK (others are Maxell from US). Any idea why I can’t capture the sound?

Are you listening to the tape while it is recording?

no, I’m not listening.

Perhaps the tape recording is faulty.

All cassettes sound good when played on the Marantz.

I’ll take a guess…

A broken ground wire (usually in the cable) can sometimes set up a “differential” connection where the left & right are subtracted. This creates a “vocal remover” effect on stereo recordings and with a mono recording almost everything will get removed except the analog noise which is random and uncorrelated on the left & right sides.

So, try one of the good tapes again. But unplug one of the RCA connectors while you’re recording. If the ground is OK, the other channel should be unaffected. If something “unexpected” happens, try another cable.

…Of course, if that turns-out to be the problem you’ll need to record the “good” tapes again.