legacycentral bbs

I have my legacy 1991 turbo, which I bought with a Pioneer radio, now I installed my old factory stereo and installed two front speakers (Pioneer), it sounds great but my volume downs every time my wipers start working, I presume it's something electrical, I know it's a stupid question but maybe someone knows how to fix it or had experience on radios.

Regards,

I would check the radio grounds.