Rb25 alternator issue

[240sxrb25]

Everytime I start my rb25 cold or hot it whines and puts out 11 volts until I rev it up to around 2k rpm or so. Then the whining stops and the charge is just over 14.

I have battery in trunk with 2 gauge I believe

[Sileighty_85]

Belt is loose,

Tighten belt