Tshark: suppress random line numbers

Hi all, I'm using tshark (in Linux) to return only packet source MAC addresses and signal strength. Here's what I use:

tshark -i wlan0 -T fields -e wlan.sa -e radiotap.dbm_antsignal

The problem is that every few packets is prefixed by an annoying ID number. I assume that these are the same as the numbers that show up unpredictably when I run "tshark -i wlan0 -n" and get this output (I've x'd out actual addresses...):

Capturing on 'wlan0'

1 0.000000 00:02:6f:xx:xx:xx -> ff:ff:ff:ff:ff:ff

2 0.131605 00:18:d1:xx:xx:xx -> ff:ff:ff:ff:ff:ff

3 0.204522 00:02:6f:xx:xx:xx -> ff:ff:ff:ff:ff:ff

4 0.228617 -> 00:18:d1:xx:xx:xx (RA)

4 5 0.336334 00:18:d1:xx:xx:xx -> ff:ff:ff:ff:ff:ff

6 0.409324 00:02:6f:xx:xx:xx -> ff:ff:ff:ff:ff:ff

7 0.447556 -> 20:16:d8:xx:xx:xx (RA)

8 0.541174 00:18:d1:xx:xx:xx -> ff:ff:ff:ff:ff:ff

9 0.649089 -> 20:16:d8:xx:xx:xx (RA)

10 0.665628 06:02:6f:xx:xx:xx -> ff:ff:ff:ff:ff:ff

11 0.746025 00:18:d1:xx:xx:xx -> ff:ff:ff:ff:ff:ff

11 12 0.768025 06:02:6f:xx:xx:xx -> ff:ff:ff:ff:ff:ff

Notice the extra "4" and "11" Does anyone have any idea what these extra numbers are and, more importantly, how I can suppress them in my output? Thanks