Noble potmeter makes noise

[klitgt]

I recently purchesed a Noble potmeter that is more than 10 years old but never used. It's at the input of a diy preamp.

After a couple of months it has started making scrathing noises in the loudspeakers when turned up/down. More noise when turned fast, less when turned slowly or pressed inwards during turning.

The retailer claims it is because I have connected a DC coupled source without DC blocking cap in the output, a Noble MUST NEVER have DC at the input, he says .

The source in question is a NAD C542 CDP which by factory default has no signal cap at the output from the OPA2134 output buffer opamps. And I can not measure any DC offset from it.

In another setup a Marantz CD7300 which measures 1.1mV DC offset feeds a similar pre with a Noble pot and has done so for nearly 2 years without problems.

Are NAD CDPs killing all Noble pots all over the world or what may be the troulbe here?