1.5 Amp load on 7805 would also in short interval from cold power on till thermal shutdown kicks in within the 7805. Long ago I had a 7805 circuit that had too much load and the cirucit board acted like low frequency thermal oscillator as 7805 forst shut down, cooled, recovered, and subsequently shut down again....Ran at about 0.3 Hz I believe.....Of course it varied with air movement around the board.

Michael Karas