Just searching for 7660 on PedalPCB I found quite a few references, many mentioning the 7660SCPAZ. I've found the meanings of the suffix letters after the S - C is temperature range (0-70 deg C), PA is package (8-pin DIP), Z is Pb-free. So it's just the S that matters as long as it's an 8-pin DIP.
Ah, just found this: "Use your digital multimeter to make sure you have a connection between pin 1 and pin 8 on your charge pump IC. If that is connected and you are hearing a whine you likely have bad chips and can fix your problem by replacing them with something from another source." Can't post a link to it (it's verboten, don't know whether by BC or PedalPCB) but if you search for 7660 it's a topic called "Problem IC Sunflower Fuzz". So maybe you have a duff 7660. I haven't really used mine so don't know if I have the same issue.