Recently my psu got broken and as a result i bought the delta 500w one since then whenever electricty wents out the UPS is making horrible noise as if a motor is running, it continues until i turn off the pc. There was no noise problem with my earlier stock psu. The UPS is 1 year old and now gives only 10min of backup,it used to give 25~30min when new. Anyone has any idea why this is occuring??