Faint lines on Ovulation Tests.

Is it normal to recieve faint lines before detecting the surge? Ive been testing since about 4 days after my period ended bc i have ovulated early in the past and missed it. Theyve all been faint so im assuming it just indicates that the test is working but has anyone taken opks and not recieved a line at all? Im still fairly new to using them so I appreciate all the knowledge I can gain from you ladies! TIA!