4 red pulsing lights fly over Portland

My friend and I left an apartment in downtown Portland near Jeld Wen Field to walk back to his apartment on SW 14th Ave. 
 When we got to the apartment, from the parking lot we saw a red pulsing light appear from over the west hills moving southeast.  
This craft was followed by another craft that looked the same.  They flew slightly faster than an airplane and at a lower altitude.  
When these two flew out of sight, another red light appeared from over the west hills followed by another one at the same distance as the first two flying in a similar direction although slightly lower in altitude and more south in their direction but still flying southeast.  
There seemed to be a low sound but it was hard to hear because we were standing right near the 405 freeway in between Salmon and Taylor St. 
It was difficult to tell how large the objects were but they seemed to be around the size of a small plane.  They were bright red and seemed to pulse at a rate close to human heart beat so the light was emitted constantly. 
 There were planes in the sky at the time but much higher in altitude with small blinking red and white lights and on a different path. 
I have never seen planes in the sky travelling on the same path as these 4 red lights.