Hello David. A fuel pump that is pulling through a clogged up filter will
whine.Quite loudly.You cant mistake it and it gets worse. Much like list
members talking about seized up engines,or list members talking about list
members who talk about seized up engines.Have you been poking around the
engine compartment? Check for wires that are not attached tightly. Maybe a
vaccum hose has fallen off. Or a vaccum hose with a burn hole in
it.Perhaps, if your fuel system was super crudded up, a bit of goop was
dislodged,and is causing a problem (doubt it). Maybe try another
strong,concentrated, can of FI cleaner.If your system is super crudded
up,maybe the other maintence items are not far behind. Like an  air filter?
You can remove the air filter and see if there is any difference.  How is
your MPG? I would suspect the timing,but you say nothing else was touched.
I dont know air cooled, but these above fixes are common to all vehicles.:>)