Grimace: Most likely the noise is created by release compounds that have hardened over 50+ years to the likes of concrete. No easy solution to the problem, not even steaming works well enought to remove that "concrete".
One note on Steam Cleaning LPs. Just steaming and micro cloth drying is ok for very clean recordings. But, as the guy that perfected and published the merits of steaming in audio mags long before others got on the bandwagon, be careful going solo without record cleaning fluids. Steam alone is not a cure all however, with the proper technique,the correct brushes, a RCM and rinsing, most(not all) substances can be removed. As noted on the Steaming Thread products such as "last" and "Sound Guard" age leaving a hard impossible to remove "concrete" that sounds just terrible. It is for that reason I dumped every MoFi release I had that was "Lasted" at the factory. Complete waste of good money but 30 years ago who knew.
One note on Steam Cleaning LPs. Just steaming and micro cloth drying is ok for very clean recordings. But, as the guy that perfected and published the merits of steaming in audio mags long before others got on the bandwagon, be careful going solo without record cleaning fluids. Steam alone is not a cure all however, with the proper technique,the correct brushes, a RCM and rinsing, most(not all) substances can be removed. As noted on the Steaming Thread products such as "last" and "Sound Guard" age leaving a hard impossible to remove "concrete" that sounds just terrible. It is for that reason I dumped every MoFi release I had that was "Lasted" at the factory. Complete waste of good money but 30 years ago who knew.