@dhcod , acoustic feedback occurs at a specific frequency and is a steady tone typically described as a howl.
Rumble is very low frequency and lumpy for lack of a better term. It is low frequency garbage for either the bearing of your turntable or the bearing of the lathe that cut the Lacquer your record was produced from. If it is your turntable it will be consistent and occur with every record. If it only occurs with some records and not others the fault lies with the manufacturer of the record.
You hear it now because your new speakers are capable of reproducing those very low frequencies. Rumble is one of the banes of vinyl reproduction like scratches, ticks and pops.