Hi
without hearing it it could be anything, but a few possibilities though not specific to supras are;
1 inlet gasket leak screaming /whistling/usually high pitched more prominent under load.
2gaskets,hoses,intercoolers,turbine finns ect dont usualy leak/make noises till pressure has risen sufficiently to do so.
3 alternator bearings can sieze up making same sounds till total siezure.As happens on toyota range.-Try remove 1 belt at a time to eliminate various items.
4 If its a belt/bearing sound ,with alt belts ect off check w/pump+t/belt pulley for any fault.+renew if any doubt
5dont know type of motor ie man/auto/air con but the more info you can give the better.
GOGS