After worldwide rates hit all-time lows on the heels of Brexit, they consolidated in a narrow, sideways pattern until someone came up with the next plan.  That plan began to take shape in early September after some market participants interpreted European Central Bank (ECB) President Mario Draghi as dropping hints about tapering ECB asset purchases--something that would have an analogous effect to the taper tantrum of 2013.  

On the following chart, looking at the underlying candlesticks, you can see the noticeable increase in volatility at the beginning of September.  Yields immediately moved to test the long term inflection point (white line), then the lower end of the trend channel (teal dotted line), and now have returned to the long term inflection point to wait out the time until the ECB's next major communication.

The communication in question will happen tomorrow morning during Draghi's press conference which begins at 8:30am.  Between now and then, we shouldn't expect yields to stray too far from the white line.

Smaller-scale market movers can cause some intraday volatility, however.  Chief among these for today is a rather large sovereign bond issuance from Saudi Arabia.  Think of this in similar terms to corporate debt issuance (and if you're not sure how to think of corporate debt issuance and its effect on mortgage rates, read this).  

In addition, actual corporate debt issuance has been ramping up this week, which could also be adding to pressure on bond markets.  The takeaway is perhaps somewhat positive in that Treasuries and MBS are holding up fairly well considering the headwinds suggested by elevated supply elsewhere in the bond complex.